6V Battery Life. Costco Interstate vs Trojan Pacer

[garyb1st]

Just watched a youtube video comparing these two similarly priced batteries.  The presentation was made by a self-described Battery Guru.  The first thing he said that caught my attention was this. While most people believe a battery should only be discharged 50%, a 6V battery can be discharged to 80%.  He didn't say if or how that effects the number of battery cycles.  Then he stated that the Trojan battery which have fewer amp hours, 210Ah vs 232 for the Interstates, can be discharged 500 times.  The Interstate batteries can only be discharged 300 times.  So a couple questions.

Can 6v batteries be discharged to 80% without shortening the life of the battery. 

Can a Trojan Pacer be discharged that many more times than a Costco Interstate battery. 

 

[Back2PA]

Can 6v batteries be discharged to 80% without shortening the life of the battery. 

Batteries can certainly be discharged below 80%.

I know there are a lot of people who subscribe to the 50% rule, I've read a couple saying you shouldn't discharge below 75%. To some degree I think it's a little like tires - used to be the "10 year rule", now 7 years is generally accepted, and I've even seen some recommend you should start thinking about tires in 3 years. You're buying the batteries to use, not to store. Many here have reported getting 7+ years out of batteries that are routinely depleted to well below 80%.

When I bought my Trojans for the last rig I had, I purchased them at a massive battery warehouse in the Phoenix area - that's all they did, batteries. Massive, massive warehouse with anything from golf cart to huge batteries that required a forklift to lift just one. They obviously serviced golf carts, but one of their main businesses was offgrid and standby battery banks - one assumes they know batteries.

I spoke for quite awhile to the service manager there, and asked about min SOC, and the accepted 50% rule. He shook his head and said that wasn't entirely correct, that they often discharged below that number with no ill effects as long as the battery was immediately brought back to 100%. By immediately he said the next day, so he was talking about overnight discharges. When I asked about minimum voltage, he said 5.9V (6V) or 11.8V (12V) was an acceptable absolute minimum that would not harm the battery.

I'm just the messenger.

 

[Utclmjmpr]

Battery life expectancy in the RV world is totally dependant on the user,, and they come in all varieties.>>>Dan

 

[Gary RV_Wizard]

The concept is simple but the practical application is not. The principle is "the deeper the discharge, the greater the impact on cycle life". Further the relationship between depth of discharge and cycles is a curve, not a straight line. In other words, the impact is not in the same proportion as the discharging. Each battery is a little different too, so you need rigorous laboratory tests to give truly accurate advice for any given battery.  It's also true that the longer the battery remains discharged, the worse the impact becomes.  Like a sick man in a hospital, the longer it lays around the more difficult the recovery gets and the chances of complete success get slimmer. 

The "50% rule" is a very broad rule of thumb intended to shortcut all the techy stuff and apply to most common batteries, but because of that it cannot be real accurate. It ranks with "Don't bring a knife to a gun fight" as sage advice even if not always strictly accurate.


Every battery also has a given number of charge cycles in its useful life. Heavy duty plate & cell construction yields more cycles and all golf car batteries are built for heavy duty in comparison to a car starting battery. Trojan, however, is one of the top industrial battery brands and typically at the higher end of the cycles scale. Therefore Trojans will generally perform longer given similar care.

The AH rating is strictly a matter of how much lead plates are inside the case. The amount of electricity that can be stored in a given amount of lead & acid is rigidly determined by the physics of lead acid chemistry.  Lead is expensive, so the lead content and therefore the AH capacity is governed by the price point of the battery. Trojan makes both 210 and 230 AH models, so they can compete in different price ranges. 

 

[Henry J Fate]

I assume that lead acid batteries are being discussed.

There is no difference in battery life between a 6 volt battery and a 12 volt battery made of the same construction and same usage. I did not watch the video but if that was being implied, I would be skeptical of any other information the video is providing.

Battery life and its quality of life is an expression of usage, age and construction.

It is not good to discharge a battery and it is not good to leave it discharged. The deeper the discharge, the less life the battery will provide. Recharging is important. Batteries should be recharged as soon as possible. The longer a battery sits discharged, the more damage is done.

Cycle ratings should be used as a guide but not as law. The cycles that users experience after purchasing a battery will differ greatly than the cycles being used in a controlled environment for a cycle rating. Thus, the actual number of cycles will also differ. 

 

[Mark_K5LXP]

...the relationship between depth of discharge and cycles is a curve, not a straight line. In other words, the impact is not in the same proportion as the discharging. Each battery is a little different too, 

Good post, Gary.  Correct, but I think it's useful to point out that for true deep cycle batteries (T105, et al) that curve is little more than a "bump".  The delivered Ah delta between 50% and 80% DOD is less than 10%.  So for the sake of less than 10% potential capacity you have throngs of "50%'ers" that repeat the dire consequences of crossing that line on the various forums (you'll KILL the batteries).  Batteries aren't heirlooms.  No different than tires and engine oil - a consumable that has a finite life.  Use it or lose it. 

People obsess about "cycle life" when the focus should be on proper charging and storage.  It takes a concerted effort to actually wear a battery out before it ages out.  Sitting dead, chronic under and over charging and neglecting water levels account for far greater battery failures than 50% vs 80%.  The only hard and fast number to watch is to never go below 10.5V under load.  If you take care of the water and charging the most cost effective battery you will ever have is one you use up. If it happens sooner due to deep cycling, congratulations- you got everything it could give.

Mark B.
Albuquerque, NM

 

[garyb1st]

Good discussion with good information.  When I first started RVing, I didn't know anything about battery maintenance.  As a result of my inexperience, I would go through a two 6v batteries every 2 years or so.  Over the years I've learned the importance of proper maintenance and charging.  The house batteries in our motorhome are approaching 3 1/2 years old.  They are in good condition and I maintain them on a regular basis.  That includes checking the water level monthly and keeping them fully charged.  I also have a Victron monitor which I check daily.  When not traveling the motorhome is plugged in to our homes 120v power.  The motorhome has a 3 stage charger so I am not concerned about overcharging. 

What prompted me to make this post is the video I watched which seemed contradictory to some of the things I've learned.  I've always tried to limit discharge to 50%.  But if I'm not shortening battery life by going down to 70 or 80%, why not.  However it seems based on some of the posts, there's not much to be gained by doing so and in my situation, no real need.  So I'll leave the depth of discharge issue at that. 

However, 300 vs 500 cycles doesn't make sense to me.  Is there really that much difference between two similar batteries.  Both in the test were 6v golf cart batteries.  If that is correct, it's a no brainer, go with the Trojans.  While the Interstates had more Ah's, I can't imagine that would cause the battery to have considerably fewer cycles. 

 

[John From Detroit]

A few times I ran my OEM interstates down into the deep OH CR**!!!! levels (total voltage under 9 volts) and they recovered and kasted 9 years total,  Done it once with the replacements (They are DEKA)

Now MARINE/deep cycle.. I'd not suggest you try it

 

[Mark_K5LXP]

if I'm not shortening battery life by going down to 70 or 80%, why not.

The batteries will die sooner if you cycle them deeper.  But you're just using what capacity they have more quickly, so you're still getting your money's worth.  When you factor it's also a race against time and if you don't use them up, you're taking capacity to the recycler.  So in my view, better to burn out than fade away. 

300 vs 500 cycles doesn't make sense to me.  Is there really that much difference between two similar batteries.

Yes.  Batteries are made for specific applications and manufacturers can tweak a number of characteristics to target anything from weight, cycles, capacity, internal impedance, water use to delivered price.  The devil's in the details and some nuances of details don't make the spec sheet. 

Both in the test were 6v golf cart batteries.  If that is correct, it's a no brainer, go with the Trojans.

In a past life I tried a number of different types of 6V golf cart batteries for my application.  In all fairness I was using them outside their rated specification but some were clearly more durable than others even though they were very close in terms of Ah and cycle specification.  The Trojans were the only ones to survive even close to their rated life, Interstates were the worst.  So not all batteries are created equal and generally you get what you pay for.  If the application doesn't demand a particular feature then no reason to pay for it.  I'm running Interstate GC-2's in the RV and they're more than adequate for what I need there.  So you weigh the benefits and the cost and go with what meets your needs best.

Mark B.
Albuquerque, NM

 

[solarman]

People obsess about "cycle life" when the focus should be on proper charging and storage.

Mark B.
Albuquerque, NM

quite true.. in previous conversations i had with Trojan engineers their number one failure point on returns
was sulfation due to under charging. they even mentioned that increasing cell charge voltage was considerably
better than under charging, but few charger makers would increase voltages in fear of overcharging.. !

certainly for solar increasing bulk/absorb voltages will help. i have spoken about this in previous posts on the solar section.

 

[Mark_K5LXP]

certainly for solar increasing bulk/absorb voltages will help.

I think you're right, either the chargers are using legacy setpoints or they're picking average or lowest common denominator values that just aren't quite there for complete cycles.  I'd have to see if I can pull up an old Trojan data sheet but the current ones seem to reflect higher absorb and equalization voltages than I remember.  This stuff is rather easy to manage when doing it manually but it's when you automate it, things drift off if you can't dial the charger in to your particular set of batteries. 

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

I think Mark has given excellent advice on the practicality of battery usage in RVs vs the 50% "rule".  I particularly like these two:

So for the sake of less than 10% potential capacity you have throngs of "50%'ers" that repeat the dire consequences of crossing that line on the various forums (you'll KILL the batteries).  Batteries aren't heirlooms.  No different than tires and engine oil - a consumable that has a finite life.  Use it or lose it.

The batteries will die sooner if you cycle them deeper.  But you're just using what capacity they have more quickly, so you're still getting your money's worth.

 

[solarman]

I think you're right, either the chargers are using legacy setpoints or they're picking average or lowest common denominator values that just aren't quite there for complete cycles.  I'd have to see if I can pull up an old Trojan data sheet but the current ones seem to reflect higher absorb and equalization voltages than I remember.  This stuff is rather easy to manage when doing it manually but it's when you automate it, things drift off if you can't dial the charger in to your particular set of batteries. 

Mark B.
Albuquerque, NM

Bulk/Absorb is now suggested at 2.47 V per cell and float at 2.25 V for Trojan cells.

for RV solar I would recommend higher, so for 12 V set bulk/absorb to 14.9 V and then check SG at the end of the day.
if the SG is low then increase voltage a little, if high then reduce..  most Rv solar i have seen is under paneled so eliminating the
3 stage charging method will get maximum watts into the battery bank. it's better to overcharge a little than to constantly under charge and sulfate.
overcharge will always give you full power, sulfation will always leave you short..


3 stage is only effective on shore power, there are not enough sun hours in a day for a complete 3 stage on solar. some will
argue this, but they are the minority with correctly designed or over paneled systems..

 

[Lou Schneider]

Handy Bob https://handybobsolar.wordpress.com/ has been saying the same thing about most RVers not fully recharging their wet cell batteries for about 20 years.

I took his advice and modified my Progressive Dynamics Converter and Charge Wizard in 2005 to let me dial in higher voltages to fully charge a set of 4 golf cart batteries.  They lasted 7 years before I replaced them on principle.

 

[River-Runner]

So to what level did you adjust the voltage rates and what was the procedure?

 

[grashley]

So to what level did you adjust the voltage rates and what was the procedure?

X2

 

[garyb1st]

Lou, IIRC, ours is a WFCO.  I've looked at it once but don't recall seeing anything that would allow me to adjust the voltage.  In looking at the motorhomes built in meter, I've seen the batteries being charged as high as 14+ volts. 

Are all converters adjustable?

 

[Gary RV_Wizard]

Are all converters adjustable?

No, it's actually rare that they are.  Some have multiple, pre-planned charging profiles with slightly different voltage levels and timing, but few have a user-adjustable voltage.  If it's a multi-stage charger it's not a simple dial-a-volt, plus there is a real danger of damage to the batteries or other electronics if the voltage is set too high.  Not the sort of liability risk a converter manufacturer wants to run in todays legal climate.
Note that Lou said he modified his converter to adjust it.

 

[garyb1st]

Thanks Gary. 

 

[SargeW]

My Magnum 3000 seems to keep the batteries pretty well topped off. As I check right now, the house batteries are showing 13.4 volts while plugged in to shore power.  And there is an equalization phase I can manually initiate. I will usually run the equalization phase about every 6 months, or within a few days of adding water to the cells.